cgroup: Fix cgroup_subsys::exit callback

Make the ::exit method act like ::attach, it is after all very nearly
the same thing.

The bug had no effect on correctness - fixing it is an optimization for
the scheduler. Also, later perf-cgroups patches rely on it.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Paul Menage <menage@google.com>
LKML-Reference: <1297160655.13327.92.camel@laptop>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index ce104e3..38117d9 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -474,7 +474,8 @@
 			struct cgroup *old_cgrp, struct task_struct *tsk,
 			bool threadgroup);
 	void (*fork)(struct cgroup_subsys *ss, struct task_struct *task);
-	void (*exit)(struct cgroup_subsys *ss, struct task_struct *task);
+	void (*exit)(struct cgroup_subsys *ss, struct cgroup *cgrp,
+			struct cgroup *old_cgrp, struct task_struct *task);
 	int (*populate)(struct cgroup_subsys *ss,
 			struct cgroup *cgrp);
 	void (*post_clone)(struct cgroup_subsys *ss, struct cgroup *cgrp);